#include<iostream>
using namespace std;
//整数a，整数b。
int sum(int a,int b=20)
{
    int result;
    result=a+b;
    return result;
}
int main()
{
    int a=100;
    int b=200;
    int result;
    result=sum(a,b);
    cout<<"和为："<<result<<endl;
    result=sum(a);
    cout<<"和为："<<result<<endl;
    return 0;
}
